Oxygen

Oxygen (O2) is a gas that is needed by the player to survive. When diving the player uses a reserve of oxygen that diminishes over time. The Oxygen reserve automatically replenishes whenever the player comes back to the surface, enters a submarine, or a seabase. Oxygen can also be replenished by swimming through bubbles produced by Purple Brain Coral.

The HUD indicator for the player's Oxygen supply is on the left side of the screen. The player has a base reserve of 40 units of Oxygen but this can be expanded by using tanks which allow an additional 30 units for every tank used. The maximum Oxygen supply is 400 units after using 12 tanks. When the Oxygen reserves are empty, the screen slowly fades to black and after about 6 seconds, the player dies and respawns.

In all non-Hardcore game modes, there are alerts for when the player has 30 seconds and 10 seconds of Oxygen remaining. However, the 30 seconds alert doesn't play unless the player has a tank equipped.

Depth is a factor that effects Oxygen consumption. When diving less than 200m the player will consume one unit per second however when diving 200m or deeper the consumption is two units per second. While the depth effect is supposed to be counteracted by equipping a Rebreather as of 07/05/15 the rebreather does not affect Oxygen consumption.